From: Konstantin Khlebnikov <koct9i@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
John Ogness <john.ogness@linutronix.de>,
Petr Tesarik <ptesarik@suse.cz>,
x86@kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] printk/panic/x86: Allow to access printk log buffer after crash_smp_send_stop()
Date: Thu, 18 Jul 2019 14:07:20 +0300 [thread overview]
Message-ID: <CALYGNiMnqUKxKsY1JRi075xs-P_QzfA4Pg3XANiW0mFYkp_RQQ@mail.gmail.com> (raw)
In-Reply-To: <20190718104756.GA22851@jagdpanzerIV>
On Thu, Jul 18, 2019 at 1:48 PM Sergey Senozhatsky
<sergey.senozhatsky.work@gmail.com> wrote:
>
> On (07/16/19 09:28), Petr Mladek wrote:
> [..]
> > +int printk_bust_lock_safe(bool kdump_smp_stop)
> > {
> > if (!raw_spin_is_locked(&logbuf_lock))
> > return 0;
> >
> > - if (num_online_cpus() == 1) {
> > + if (num_online_cpus() == 1 || kdump_smp_stop) {
> > debug_locks_off();
> > raw_spin_lock_init(&logbuf_lock);
> > return 0;
>
> Let me test the waters. Criticize the following idea:
>
> Can we, sort of, disconnect "supposed to be dead" CPUs from printk()
> so then we can unconditionally re-init printk() from panic-CPU?
>
> We have per-CPU printk_state; so panic-CPU can set, let's say,
> DEAD_CPUS_TELL_NO_TALES bit on all CPUs but self, and vprintk_func()
> will do nothing if DEAD_CPUS_TELL_NO_TALES bit set on particular
> CPU. Foreign CPUs are not even supposed to be alive, and smp_send_stop()
> waits for IPI acks from secondary CPUs long enough on average (need
> to check that) so if one of the CPUs is misbehaving and doesn't want
> to die (geez...) we will just "disconnect" it from printk() to minimize
> possible logbuf/console drivers interventions and then proceed with
> panic; assuming that misbehaving CPUs are actually up to something
> sane. Sometimes, you know, in some cases, those CPUs are already dead:
> either accidentally powered off, or went completely nuts and do nothing,
> etc. etc. but we still can kdump() and console_flush_on_panic().
Good idea.
Panic-CPU could just increment state to reroute printk into 'safe'
per-cpu buffer.
>
> -ss
next prev parent reply other threads:[~2019-07-18 11:07 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-16 7:28 [PATCH 0/2] panic/printk/x86: Prevent some more printk-related deadlocks in panic() Petr Mladek
2019-07-16 7:28 ` [PATCH 1/2] printk/panic: Access the main printk log in panic() only when safe Petr Mladek
2019-07-17 9:56 ` Sergey Senozhatsky
2019-07-18 8:36 ` Petr Mladek
2019-07-18 9:49 ` Sergey Senozhatsky
2019-07-19 12:57 ` Petr Mladek
2019-07-23 3:13 ` Sergey Senozhatsky
2019-07-24 12:27 ` Petr Mladek
2019-07-31 6:08 ` Sergey Senozhatsky
2019-07-31 6:59 ` Sergey Senozhatsky
2019-07-18 10:11 ` Sergey Senozhatsky
2019-07-16 7:28 ` [PATCH 2/2] printk/panic/x86: Allow to access printk log buffer after crash_smp_send_stop() Petr Mladek
2019-07-18 10:47 ` Sergey Senozhatsky
2019-07-18 11:07 ` Konstantin Khlebnikov [this message]
2019-07-18 11:29 ` Sergey Senozhatsky
2019-07-19 12:19 ` Petr Mladek
2019-07-18 9:59 ` [PATCH 0/2] panic/printk/x86: Prevent some more printk-related deadlocks in panic() Konstantin Khlebnikov
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